1. Technical Field
The present invention relates to a nitride-based light emitting device, and more particularly, to a nitride-based light emitting device which can relieve strain in an active layer to improve light emitting efficiency.
2. Description of the Related Art
Generally, nitride semiconductor light emitting devices may generate light in a wide range including UV, blue and green ranges. In particular, GaN-based nitride semiconductor light emitting devices are applied to optical devices for blue or green light emitting diodes (LED), high speed switching devices, such as metal semiconductor field effect transistors (MESFET), hetero junction field effect transistors (HFET), and the like, and high output devices.
Such a nitride-based semiconductor light emitting device has a hetero structure wherein an active layer of a multi-quantum well (MQW) structure having InGaN quantum-well layers is interposed between an n-type nitride semiconductor and a p-type nitride semiconductor. Here, the wavelengths of light such as blue, green and the like are generally determined according to the indium (In) content in the InGaN quantum-well layers.
The MQW structure active layer comprises plural pairs of an InGaN quantum-well layer and a GaN quantum-barrier layer. However, the MQW active layer undergoes severe strain between the InGaN well layer and the GaN barrier layer due to lattice mismatch between InGaN and GaN. Such strain generates a large piezoelectric field in the active layer, causing reduction of internal quantum efficiency of the active layer.
In addition, strain between the InGaN quantum-well layer and the GaN quantum-barrier layer causes generation of V-pits in the active layer and provides a rough interface between the well layer and the barrier layer when forming the active layer by stacking the well layers and the barrier layers, whereby crystallinity of the active layer can be deteriorated, thereby making it difficult to fabricate a highly efficient light emitting device.
Korean Patent Publication No. 10-2009-0002567A (published on Jan. 9, 2009) discloses a nitride-based semiconductor light emitting device wherein an InGaN relief layer having a high indium content is formed between an n-type contact layer and an active layer to improve light emitting efficiency by relieving strain between the well layer and the barrier layer in the active layer.